Genetic evaluation techniques in dairy cattle

Abstract

The statistical methods used during the past 50 years for genetic evaluation of dairy bulls and cows are presented with special emphasis on the reasons which motivated their development and then their withdrawal. The selection index theory applied to data such as deviation of the cows’ records from their herdmates became obsolete because environmental effects were imperfectly corrected and the underlying genetic trend was not accounted for. The Best Linear Unbiased Prediction (BLUP) enables simultaneous estimation of genetic and environmental effects. Initially applied to simple models for sire evaluation (sire or sire-grand-sire models), BLUP is increasingly used with an « animal model » nowadays, allowing a joint evaluation of males and females. Using this method, some interesting properties are obtained. Other aspects, such as the modelling of performance records, the inclusion of several lactations and the computation difficulties involved are also tackled.